You probably would have heard of the $3.7 billion Dakota Access Pipeline that will carry about 500,000 barrels of oil per day and give the state’s producers cheaper access to refineries and other customers on the U.S. Gulf Coast.

You may have heard of the indigenous rights movement, between April and December 2016, by several thousand protesters led by members of the Standing Rock Sioux tribe arguing the oil could spill and endanger the water. You may have also heard the Dakota Access pipeline has already leaked on two occasions in 2017.

The mysterious looking structure is part of the Stanley R. Mickelsen Safeguard Complex in Cavalier County, North Dakota. The complex was the United States’ first operational anti-ballistic missile defense system, and was put into operation in the early 1970s to defend missiles based at Grand Forks Air Force Base in the event of a nuclear ICBM attack by the Soviet Union.

“The interior of the pyramid is just like the exterior, amazing, housing several underground bases where the control room and monitoring systems were located. All of those rooms were connected to a network of powerful radars across US soil.

“According to many, today, not a single human being can be seen for miles around the complex, and official statements are that the facility is completely abandoned, looking like a post-apocalyptic science fiction movie scene.”

The Library of Congress has an extraordinary set of images, taken for the U.S. government by photographer Benjamin Halpern, documenting various states of construction and completion of the massive structure that served as the Complex’s missile control building. Take a look:

The missile field and Missile Site Radar at the Stanley R. Mickelsen Safeguard Complex in Nekoma, N.D.